1. Field of the Invention
This invention relates to the processing of semiconductor lead frames and, more particularly, to apparatus for automatically aligning a lead frame and a processing device, such as a plating head for plating the pads of the lead frame.
2. Description of the Prior Art
In the plating of the pads of a semiconductor lead frame, a relatively long length of the lead frame is advanced by an indexing device incrementally past a plating head. At each stop, a number of pads are simultaneously plated. Then the lead frame is advanced by the indexing device through a selected distance, such as 9 to 11 inches, bringing new pads to be plated into the plating head. Because the indexing device is a relatively long distance away from the plating head, errors are generated in the positioning of the pads relative to the head, and these errors must be compensated for to assure that the pads are properly plated.
In the prior art, to compensate for these positioning errors the plating head has been moved minutely after the lead frame is stopped. The movement of the plating head is done manually, for example, by manual rotation of an advancing screw, by the turning of a handle, or by other similar means. These adjustments require operator attention at all times during the operation of the plating head, resulting in additional labor costs and difficulty of accurate repetition. Furthermore, human error makes accurate alignment of the pads relative to the plating head difficult.
In view of the problems mentioned above, a need exists for apparatus for automatically aligning the plating head and pads of a semiconductor lead frame after the lead frame has been moved by the indexing device, for example, following the plating of a group of pads in the plating head. The present invention satisfies the aforesaid need and provides apparatus which is simple and rugged in construction, highly reliable, and requires substantially no operator attention.